U.S. high-yield bond funds suffered the biggest outflows in more than two years as investors reassess risk after the best returns in a decade and an uncertain outlook due to the pandemic.

High-yield investors pulled $5.55 billion during the week ended July 1, according to data compiled by Refinitiv Lipper. It’s the fourth-biggest withdrawal on record and compares with an outflow of just $87.6 million the prior week.

“You’ve seen high yield recover so much during the quarter that it has coaxed some money out of the asset class,” said Scott Kimball, a portfolio manager at BMO Global Asset Management.

About $5.1 billion was pulled for the week ended March 4 when the spreading coronavirus was battering markets globally, but that was soon followed by about three months of inflows after the Federal Reserve unleashed unprecedented support in the wake of the outbreak.

Investors are cutting back on risk after high-yield debt returned 10.2% in the second quarter, the most since 2009, according to Bloomberg Barclays index data. Average yields have fallen to just 6.77% as of Wednesday from a peak of 11.69% on March 23, the data show.

The rally has also spurred a surge in corporate borrowing with high-yield issuance reaching a record monthly high of more than $58 billion in June. But much of the outlook depends on how the pandemic impacts the economy in the second half, with some analysts warning that U.S. credit could be susceptible to weakening.

John McClain, a portfolio manager at Diamond Hill Investment Group, expects investors to continue reaching for yield and for returns to remain attractive.

“Given the strong flow into the asset class in the quarter, combined with strong returns, investors are taking some chips off the table. We see this as short-sided,” said McClain.

Many riskier high-yield companies are currently exceeding the modest expectations that they had set for investors when the pandemic started to spread earlier this year, said Ken Monaghan, co-head of high yield at Amundi Pioneer Asset Management.

If virus cases drop and there’s no second wave, then big parts of the economy can reopen, and junk bonds can surge. But if cases continue to jump or an accessible vaccine or treatment takes longer than expected, the virus will keep harming the economy and have an impact on riskier credit.

This is the second consecutive week of outflows from high-yield funds. Investors pulled $427 million from leveraged loan funds, the third straight outflow.